We need to go beneath the surface and engage the whole mind - think holistically - to achieve the change we seek, says Eric Harrison I'm not a believer. I try not to believe in anything. My world divides up into what I know and what I don't know. There is no need for me to believe in what passes for factual, well-supported truth, and as for the rest, I need to have a good reason for any hypothesis.

If the grounds are too fragile for any idea, I can't take it seriously at all. This is not to say that I am immune from the gravitational pull of simple answers and consoling beliefs. Their Platonic purity has enormous aesthetic appeal, similar to the perfect cadence that ends a piece of music. Even the full stop that ends the little journey of a sentence feels satisfying and authoritative. Keats said, "Truth is beauty and beauty truth" but those were the words of a very young man. Elegance looks convincing but it is never proof. A well shaped sentence or an inspirational idea is no guarantee against nonsense.

Each day I learn more, but the ratio between what I know and what I don't know expands at an ever increasing rate. This seems to be a law of knowledge, for me at least. The more I know and the wiser I become, the more I glimpse the astronomical scale of my ignorance. I find this prospect both delightful and alarming. I don't think I will ever get bored by reaching the end of the line. Indeed, an alignment to uncertainty and an openness to doubt seems to be a hallmark of any truth worth considering.

Most of the world's common beliefs have no relation to fact and don't seriously pretend to. If God, or life after death, or free market economics were facts, we wouldn't need to believe in them. Religion, politics, spirituality and any number of hopefully held beliefs have the logical sophistication of children's stories. They appeal to the child in us. They exert their control and enchant us precisely because of their magical thinking and satisfying gestalts. Lord Bertrand Russell was the most famous atheist before Richard Dawkins and he said, "Man is a credulous animal and must believe something; in the absence of good grounds for belief, he will be satisfied with bad ones."

We can't help hoping and believing. It is in our nature to strive for a better life both personally and politically. It would be wonderful to have a planet free from injustice and poverty, with equality and opportunity for all. We constantly hear the call for political and spiritual leaders with vision who can inspire us, so we shouldn't be surprised that so many imposters try to answer that call. We need to believe that it is possible to improve our world, if only to avoid getting bogged down in the despair and confusion of this one.

Yet there is no question that this kind of optimistic belief has tremendous capacity to do evil. The past century saw some of the most visionary leaders of all time, namely Hitler, Stalin, Mao and Pol Pot. For them and their millions of dedicated followers, the vision of what they were trying to achieve was nothing less than the new Jerusalem. It was the direct descendent of the transcendental religious fervour of the previous centuries.

The Nobel Prize winner Friedrich Hayek was very conscious of the dangers of too much vision and confidence. "To act on the belief that we possess the knowledge and power to enable us to shape the processes of society entirely to our liking, knowledge which in fact we do not possess, is likely to make us do much harm."

As an economist who had endured two world wars, Hayek believed in positive social change, but he had clear ideas about how this should not be attempted. He said we have to use our knowledge, not as a craftsman who shapes a finished product, but as a gardener whose skill is limited to providing the best conditions for his plants.

This metaphor makes sense to me. When I was young, I became a good gardener over a period of about five years. I soon found I could count on good crops overall, but I could never guarantee good tomatoes or good nectarines in any particular year.

This same logic applies at a psychic level. The idea that we can have direct control of our minds by manipulating our beliefs is similar to the central command fallacies of fascism, communism and evangelical religions.

The brain is wired to operate like a democracy, not a dictatorship. Democracies are chaotic but they work because they give considerable freedom to the individuals and groups within them. Democracies tend to have functional rather than visionary goals. They give us better roads and education even if they neglect to rid the world of evil. Dictatorships, on the other hand, concentrate god-like powers in the hands of a few and eventually become rigid and collapse. Trying to control our minds from the top down has a similar effect.

Despite the evidence, we like to think that we are in control of our minds, or could be if we tried harder. This fallacy is reinforced by the subject-verb-object structure of the basic sentence. The "I" stands, godlike and upright, at the head of the sentence. This indivisible prime mover then initiates an action towards a planned outcome. It seems so obvious. We've lived with this kind of logical, "I do" progression ever since we learnt to talk.

So why is it that so many actions go wildly wrong? Why do other forces so often knock aside the "I" and take over? And why does so much mental activity seem to happen with no "I" in sight?

The psychologist Robert Hillman had an insightful answer to this. He studied with Carl Jung who argued that for psychic health we needed to go beyond the surface turbulence and contact what he called the "Self" within us.

Hillman went a step further. He said that it is better to think one's psychic integrity as being more like that of a family than an individual. His example was the 12 Greek gods; Zeus was the pater familias of this warring tribe of brothers, sisters, wives and husbands and children. They enjoyed great drunken parties together but never saw eye to eye. They formed alliances against each other for passing gain. They supported human champions on either side of the Trojan War, and they were even able to gang up against Zeus himself.

This model of the psyche explains why the "I" can't exert perfect control. The "I" is just the constitutional monarch, or the chairman of the board, or the apologist for what has already happened, or the strongest in a team of strong players. The most successful "I" is not the visionary leader. It is the skilful negotiator who can marshal forces larger than himself towards a common goal.

The mind is operated by a team of specialists, each with its own cubbyhole in the brain. Individually, they handle memory, language, thought, emotion, drive, concentration and co-ordinated quality control. They constantly inhibit or reinforce or just chatter to each other through a process that is called regulatory feedback or "reverberant reentry". Each member of the team on its own would be utterly useless. Put them together, and let them haggle for acceptable outcomes, and the results can be miraculous.

Most beliefs are more or less harmless. We can have decorative beliefs, like wallpaper, that mirror part of our soul back to us. Once a belief starts to affect our behaviour, however, its potential for damage should be acknowledged. A healthy belief is one that has a good dialogue with doubt and opposing points of view. Beliefs should be provisional until the facts or better theories come in. Fixed beliefs, or those that regard doubt as a moral weakness, are virtually guaranteed to produce narrow mindedness, if nothing worse.

Some people dramatically change their lives for the better, and a key driver is that they believed it was possible. We look at them and think, "I could do that too." Without that kind of hope, we would stay in our ruts. Even if we haven't been able to escape drinking or over-eating or depressive tendencies in the past, we know it is possible by observing what others have done.

A belief that we can change if we try hard enough is a necessary starting point - but it won't do it on its own. Researchers have repeatedly shown that willpower is a limited resource that gets fatigued over the day just as muscles do. The more frequently you resist a temptation, the more vulnerable you become to the next one. Repeated exposure is almost guaranteed to break us down, as torturers know.

The best kind of belief is one that stays as close as possible to the facts. Experience tells us that positive change is possible but not necessarily easy. It usually takes cunning, persistence and self understanding. It needs most of that team of specialists in the brain.

The sunny optimist ("I can do it!") in the left hemisphere needs to listen to the moody right hemisphere. The memory bank reminds us what will happen if we do or if we don't. The emotional brain pumps out the necessary enthusiasm and persistence. The bullshit detector tells us when we're talking nonsense or trying to ignore our injuries. The storeman tells us when our energy is depleted, and the palace guards fight off the rabble. We certainly need vision, but it is this motley crew of disparate characters that actually does the work.